Here are a few handy commands you may need when troubleshooting vSphere issues and iSCSI.
You can use the following commands to check dead paths, rescan HBAs, and more.
To see the last part of vmkernel log: less /var/log/vmkernel
List all paths with details: esxcfg-mpath -l
List all vSwitches and Port Groups: esxcfg-vswif -l
List all devices with corresponding paths: esxcfg-mpath -b
Rescan a particular HBA: esxcfg-rescan vmhba33
Ping the target: vmkping 188.8.131.52
Get dead paths: esxcfg-mpath -l grep -i dead
Report information on fist volume: vdf -h